Rubber composition usable in the vulcanized state as a tire safety support and such a support

ABSTRACT

The present invention provides a rubber composition which when vulcanized may be used to form a safety support intended to be mounted on a wheel rim within a tire. The invention also is directed to such a support, capable of supporting a tread of the tire in the event of a drop in inflation pressure, and to a mounted assembly comprising this support. A rubber composition according to the invention comprises (phr: parts by weight per 100 parts of diene elastomer(s)): (a) a diene elastomer, (b) particles of an α-olefinic thermoplastic polymer having a melting point greater than or equal to 150° C., in an amount of 5 to 30 parts by weight per 100 parts diene elastomer (phr), wherein the mean size by weight of the particles is between 50 μm and 500 μm, (c) greater than 60 phr of reinforcing filler, and (d) from 3 to 8 phr of sulphur.

BACKGROUND OF THE INVENTION

The present invention relates to a rubber composition that, in itsvulcanized state, may be used in a safety support intended to be mountedon a wheel rim within a tire. The invention is also directed to thesafety support, which is capable of supporting a tread of the tire inthe event of a drop in inflation pressure and to a mounted assemblycomprising the support.

Safety supports for vehicle tires are intended to be mounted on a rimwithin the tire for the purpose of supporting the tread of the tire inthe event of a loss of inflation pressure. Such supports comprise a basewhich is intended to conform to the rim and a crown which is intended tocome into contact with the tread in the event of loss of inflationpressure, but leaves a clearance relative thereto at nominal pressure.

Japanese patent specification JP-A-3/82601 discloses a safety supportcomprising a substantially cylindrical base and crown, which furthercomprises an annular body connecting the base and crown.

This annular body comprises a supporting element which is continuouscircumferentially having:

a plurality of partitions extending axially on each side of acircumferential median plane and distributed around the circumference ofthe support, and

joining elements extending substantially circumferentially, each joiningelement connecting the respective ends of two adjacent partitions whichare arranged on the same side of the support, said joining elementsbeing arranged alternately in succession on each side of saidpartitions;

in which the partitions and joining elements are substantiallyrectilinear and the difference between the maximum and minimum values ofthe area of an axial section of the support element as a function of theazimuth, relative to the sum of these same areas, is preferably lessthan 0.3. As a consequence, as a function of the azimuth, the area of anaxial section of the support element varies at most by a factor of twoin order to ensure good uniformity of loading capacity and to limitvibration when running on the support.

This support is produced from a hard polymeric material, with the wholesupporting element being designed to withstand compressive loads.

Such supports may be produced in conventional manner, for example byinjection molding.

Vulcanized rubber compositions intended to constitute part of a tire andwhich exhibit improved rigidity characteristics are also known; See,e.g., U.S. Pat. No. 5,023,301 which discloses compositions that comprisean elastomer matrix in which polypropylene fibrils of a maximum lengthof 15 μm and a reinforcing filler are randomly dispersed.

One major disadvantage of the composition is its reduced elongation atbreak in comparison with a “control” composition not containingpolypropylene fibrils (the ultimate elongation modulus is less than onethird of the corresponding modulus of the “control” composition). Suchcompositions, therefore, are not suitable for constituting safetysupports.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a rubber composition,which in its vulcanized state can be used in a safety support intendedto be mounted on a wheel rim inside a tire. The composition is such thatit provides for improved weight reduction performance for the supportover known supports at a comparable flat running service life.

The rubber composition according to the invention comprises (in parts byweight per 100 parts of diene elastomer(s)):

at least one diene elastomer,

particles of an α-olefinic thermoplastic polymer, having a melting pointgreater than or equal to 150° C., in an amount of from 5 to 30 phr,wherein the mean particle size by weight of particles is between 30 μmand 500 μm,

more than 60 phr of a reinforcing filler and

from 3 to 8 phr of sulphur.

Both the non-vulcanized and the vulcanized rubber compositions arecontemplated in the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention can be better understood with reference to theappended drawings in which:

FIG. 1 is a side view of a safety support according to one embodiment ofthe invention;

FIG. 2 is an axial section of a mounted assembly according to theinvention, in which the support of FIG. 1 is mounted on a wheel rim andis in supporting position against a tire;

FIG. 3 is a section along line AA in FIG. 1 of a supporting elementaccording to a first embodiment of the invention;

FIG. 4 is a section along line AA in FIG. 1 of a supporting elementaccording to a second embodiment of the invention which comprisespartitions connected together by alternate circumferential joiningelements;

FIG. 5, similar to FIG. 4, is a section along line AA in FIG. 1 of asupporting element, the partitions of which are of variable thickness;

FIG. 6, similar to FIG. 4, is a section along line AA in FIG. 1 of asupporting element, the partitions of which comprise a centralconnecting portion which is oriented circumferentially;

FIG. 7, similar to FIG. 4, is a section along line AA in FIG. 1 of asupporting element, the circumferential joining elements of which are ofvariable length;

FIG. 8, similar to FIG. 4, is a section along line AA in FIG. 1 of asupporting element, the partitions of which exhibit three reversals ofcurvature across the width thereof;

FIG. 9, similar to FIG. 4, is a section along line AA in FIG. 1 of anannular body including another embodiment of a supporting element, thepartitions of which exhibit three reversals of curvature across thewidth thereof;

FIGS. 10 and 11, similar to FIG. 4, are respectively sections accordingto line AA in FIG. 1 of annular bodies according to the inventionincluding supporting elements, the partitions of which are of variablethickness and having axial supporting walls;

FIG. 12 is a side view of a support according to said second embodimentof the invention, the annular body of which comprises a central web; and

FIG. 13 is a perspective view illustrating a known support architecture.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with the invention, a diene elastomer is defined as anelastomer obtained at least in part (i.e. a homopolymer or copolymer)from diene monomers (conjugated or unconjugated monomers bearing twodouble carbon—carbon bonds). One or more elastomers may be used in therubber compositions of the invention.

Preferably, the elastomers comprise at least one essentially unsaturateddiene elastomer, which is a diene elastomer is a diene elastomer whichis obtained at least in part from conjugated diene monomers having acontent of moieties or units of diene origin (conjugated dienes) whichis greater than 15% (mol %) and includes:

a) any homopolymer obtained by polymerization of a conjugated dienemonomer, such as 1,3-butadiene, 2-methyl-1,3-butadiene (or isoprene), a2,3-di(C1 to C5 alkyl)-1,3-butadiene, such as2,3-dimethyl-1,3-butadiene, 2,3-diethyl-1,3-butadiene,2-methyl-3-ethyl-1,3-butadiene, 2-methyl-3-isopropyl-1,3-butadiene, andphenyl-1,3-butadiene;

b) any copolymer obtained by copolymerization of one or more conjugateddienes with each other or with one or more vinyl aromatic compounds,such as styrene, ortho-, para- or meta-methylstyrene. Exemplarycopolymers include butadiene-styrene copolymers and butadiene-isoprenecopolymers.

According to one embodiment of the invention, the rubber compositionfurther comprises a homopolymer obtained by polymerization of aconjugated diene monomer having 4 to 12 carbon atoms, or a copolymerobtained by copolymerization of one or more conjugated dienes with eachother or with one or more vinyl aromatic compounds having from 8 to 20carbon atoms, in a quantity of less than or equal to 40 phr.

A composition according to the invention may comprise a blend ofapproximately 60 phr of natural rubber and approximately 40 phr ofpolybutadiene.

The reinforcing filler of the rubber composition according to theinvention preferably comprises a reinforcing white filler in a majorityproportion, i.e. in a mass fraction of greater than 50% of totalreinforcing filler.

A reinforcing white filler is defined as a white filler which iscapable, on its own, without any intermediate means other than a whitefiller/elastomer bonding agent, of reinforcing a rubber compositionintended for the manufacture of tires. A reinforcing white filler canreplace the reinforcement action of a conventional filler of tire-gradecarbon black.

Reinforcing white fillers include silica in an amount in the compositionof greater than 60 phr, advantageously between 60 and 80 phr. Morepreferably, the silica is present in an amount between 65 and 75 phr.

Suitable silicas include any precipitated or pyrogenic silicas known tothose skilled in the art, the BET or CTAB surface area values of whichare both within a range from 50 m²/g to 200 m²/g. Highly dispersibleprecipitated silicas are preferred.

“Highly dispersible silica” is defined as any silica having a verysubstantial ability to disagglomerate and to disperse in an elastomericmatrix, which can be observed in known manner by electron or opticalmicroscopy on thin sections. Non-limiting examples of such highlydispersible silicas that may be used in the compositions of theinvention include silicas BV 3370 and BV 3380 from Degussa, silicasZeosil 1165 MP and 1115 MP from Rhodia, silica BXR 160 from PPG orsilica Zeopol 8745 M from Huber.

Preferably, the BET or CTAB surface area values of the silica are bothin the range of between 110 and 200 m²/g and, more preferably, between140 and 195 m²/g.

The physical state of the silica may be in the form of a powder,microbeads, granules, balls, etc.

As used herein, silica includes blends of different silicas. Silica maybe used alone or in the presence of other white fillers. The CTABspecific surface area value is determined in accordance with the methodof Standard NFT 45007 of November 1987. The BET specific surface areavalue is determined in accordance with the method of BRUNAUER, EMMETTand TELLER, which is described in “The Journal of the American ChemicalSociety, vol. 60, p. 309 (1938)” and corresponds to Standard NFT 45007of November 1987.

Other non-limiting examples of reinforcing white fillers which may beused include:

aluminas (of the formula Al₂O₃), such as the high dispersibilityaluminas, described in European Patent Specification EP-A-810 258 and

aluminium hydroxides, such as those disclosed in international patentspecification WO-A-99/28376.

The reinforcing filler in the composition of the invention may alsocomprise grade 6 or grade 7 carbon black in a minority proportion, i.e.in a mass fraction of less than 50% of the reinforcing filler. Carbonblacks N683 and N772 are suitable for this purpose.

Carbon black/silica blends or carbon blacks partially or entirely coatedwith silica are also suitable as a reinforcing filler according to theinvention.

The rubber composition of the invention also comprises, a reinforcingwhite filler/elastomer bonding agent (also known as a coupling agent)when the reinforcing filler comprises a reinforcing white filler. Thepurpose of the bonding agent is to provide an adequate chemical and/orphysical bond (coupling) between the white filler and the elastomer(s)while facilitating dispersion of the white filler within the elastomericmatrix.

The bonding agent, which is at least bifunctional, has the simplifiedgeneral formula “Y-T-X”, in which:

—Y represents a functional group (“Y” function) which is capable ofbonding physically and/or chemically with the white filler, the bondbeing established, for example, between a silicon atom of the couplingagent and the hydroxyl (OH) surface groups of the filler (for example,surface silanols in the case of silica);

—X represents a functional group (“X” function) which is capable ofbonding physically and/or chemically with the elastomer, for example bymeans of a sulphur atom; and

—T represents a hydrocarbon group that links Y and X.

These bonding agents are not to be confused with simple agents forcoating the filler. Such simple agents may comprise the Y function whichis active with respect to the filler, but are devoid of the X functionwhich is active with respect to the elastomer.

Bonding agents, of variable effectiveness, have been described in alarge number of documents and are well-known to those skilled in theart. In fact, any bonding agent which is known to or likely to ensureeffective bonding between the silica and diene elastomer in rubbercompositions usable in tires, such as organosilanes, in particularpolysulphurized alkoxysilanes or mercaptosilanes, may be used.

In particular polysulphurized alkoxysilanes are used, such as thosedescribed in U.S. Pat. Nos. 3,842,111, 3,873,489, 3,978,103, 3,997,581,4,002,594 or, more recently, U.S. Pat. Nos. 5,580,919, 5,583,245,5,663,396, 5,684,171, 5,684,172 and 5,696,197.

So-called “symmetrical” polysulphurized alkoxysilanes which satisfy thefollowing general formula (I) are particularly suitable for thecomposition, without the definition below being limiting:

(I) Z—A—S_(n)—A—Z, in which:

n is an integer from 2 to 8 (preferably from 2 to 5);

A is a divalent hydrocarbon radical (preferably a C₁-C₁₈ alkylene or aC₆-C₁₂ arylene, more particularly a C₁-C₁₀ alkylene, in particular aC₂-C₄ alkylene, preferably propylene);

Z corresponds to one of the formulae below:

in which:

R¹, which may or may not be substituted, and may be identical ordifferent, represents a C₁-C₁₈ alkyl, a C₅-C₁₈ cycloalkyl, or a C₆-C₁₈aryl (preferably a C₁-C₆ alkyl, a cyclohexyl or phenyl, in particular aC₁-C₄ alkyl, more particularly methyl and/or ethyl);

R², which may or may not be substituted, and may be identical ordifferent, represents a C₁-C₁₈ alkoxyl or C₅-C₁₈ cycloalkoxyl(preferably a C₁-C₈ alkoxyl or a C₅-C₈ cycloalkoxyl, more particularlymethoxyl and/or ethoxyl).

Where mixtures of polysulphurized alkoxysilanes corresponding to formula(I) above, in particular conventional commercially available mixtures,are used, it will be understood that the mean value of “n” is afractional number, preferably varying between 2 and 5.

Particular polysulphurized alkoxysilanes include polysulphides (inparticular tetrasulphides) of bis(alkoxyl(C₁-C₄)silylpropyl),particularly bis(trialkoxyl(C₁-C₄)silylpropyl), more particularlypolysulphides of bis(3-trimethoxysilylpropyl) or ofbis(3-triethoxysilylpropyl). Bis(3-triethoxysilylpropyl) tetrasulphide,abbreviated TESPT, having the formula [(C₂H₅O)₃Si(CH₂)₃S₂]₂, ispreferably used. TESPT is sold, for example by Degussa under the nameSi69 (or X50S when supported at a content of 50 wt % on carbon black) oralternatively by Witco under the name Silquest A1289.

The person skilled in the art will be able to adjust the content ofbonding agent in the compositions of the invention, according to theintended application, the elastomer(s) used and the quantity ofreinforcing white filler used. The amount by weight of bonding agent inthe rubber compositions of the invention are within a range from 2 to15% relative to the mass of reinforcing white filler, preferably withina range from 5 to 12%.

The sulphur content in the composition according to the invention variesfrom 3 to 8 phr, preferably from 4 to 6 phr.

The rubber compositions according to the invention also contain, inaddition to the elastomer(s), reinforcing filler, sulphur and one ormore reinforcing white filler/elastomer bonding agent(s), various otherconstituents and additives usually used in rubber mixtures, such asplasticizers, pigments, antioxidants, vulcanization accelerators,extender oils, and/or one or more agents for coating the reinforcingwhite filler, such as alkoxysilanes, polyols, amines etc.

According to one embodiment of the invention, the α-olefinic polymer inthe rubber composition is isotactic polypropylene.

According to another feature of the invention, the α-olefinic polymerparticles dispersed in the elastomer(s) are substantially spherical.

The rubber composition according to the invention exhibits an M10elasticity modulus at 10% deformation which is greater than 10 MPa andis preferably greater than 15 MPa. When it is used in a safety support,the composition preferably exhibits an M10 modulus in the range of 25and 35 MPa.

The vulcanized rubber composition may be prepared as follows:

in a first thermomechanical working stage, the elastomer(s), reinforcingfiller and α-olefinic polymer in the powder state are kneaded, with thedropping temperature being approximately 155° C.,

in a second mechanical working stage, a sulphur vulcanization system isadded to the mixture obtained at the completion of the first stage, and

in a third vulcanization stage, the mixture obtained upon completion ofthe second stage is cured.

The process is carried out such that the operating temperatures of thethree stages are always below the melting temperature of the α-olefinicpolymer, such that the polymer is dispersed in the elastomer(s) in theform of substantially spherical particles.

According to one embodiment of the invention, preparation involves:

in the first stage, kneading at an initial temperature substantiallyequal to 100° C., then

in the second stage, adding the vulcanization system at a temperature ofbelow 100° C., then

in the third stage, curing at a temperature substantially equal to 150°C.

A safety support according to the invention comprises a vulcanizedrubber composition of the invention. This support comprises:

a substantially cylindrical base, intended to conform to the rim,

a substantially cylindrical crown intended to come into contact with thetire tread in the event of a drop in inflation pressure, but to leave aclearance relative to said tread at nominal inflation pressure, and

an annular body connecting the base to the crown, the body comprising acircumferentially continuous supporting element having a circumferentialmedian plane, the supporting element comprising a plurality ofpartitions extending axially on each side of the circumferential medianplane and distributed around the circumference of the support.

According to a first embodiment of a support according to the invention,the annular body also comprises joining elements extending substantiallycircumferentially on one of the sides of the support, each joiningelement connecting the respective ends of two adjacent partitions whichare arranged on the side of the support, said joining elements beingarranged alternately in succession on each side of said partitions.

In this first embodiment, the joining elements are mutually supportedbetween two adjacent partitions by a rib extending from the crown to thebase of the support such that the joining elements form a continuousjoining wall in the form of a gusset all along the side of the support.

More precisely, the joining wall comprises a plurality of cells, each ofwhich is delimited by two adjacent ribs, the bottom of each cellsubstantially exhibiting a dihedral shape, the ridge of which is formedby one of said partitions and the faces of which are respectively formedby the alternate joining elements.

According to a second embodiment of a support according to theinvention, the annular body also comprises joining elements extendingsubstantially circumferentially on both sides of the support, eachjoining element connecting the respective ends of two adjacentpartitions which are arranged on the same side of the support, thejoining elements being arranged alternately in succession on each sideof said partitions.

In this second embodiment, the partitions are modified in their centralportion relative to their lateral ends, so as to increase the bucklingresistance of the annular body under radial load.

In fact, the central portion of the supporting element is moved awayfrom the joining elements and may be destroyed during running on thesupport by the occurrence of a repeated buckling deformation. In thecase of supports manufactured from an elastomeric material, suchrepeated buckling deformation during running initiates and propagatescracking on the side of the walls subjected to extension. On the otherhand, in the case of supports manufactured from plastic materials,buckling deformation results in plastic deformation. Such irreversibledeformation considerably reduces the stiffness and the loading capacityof the structure, progressively rendering it incapable of fulfilling itsfunction.

The ratio between the thickness of the partitions in their centralportion and in their lateral ends is greater than 1.1 and preferablygreater than 1.5. The variation in thickness substantially increases thebuckling resistance of the central portion of the partitions, whichmeans that, for a given radial load, the thickness of the joiningelements may be limited and the total weight of the support may bereduced.

From one lateral end to the other, these partitions exhibit at least onereversal and, preferably, three reversals in the direction of thecurvature thereof.

These partitions exhibit, for example, a central portion extendingsubstantially axially between two lateral portions, these lateralportions meeting the joining elements and forming an angle y relative tothe circumferential direction ranging from 20 to 40 degrees.

According to another embodiment of a support of the invention, thepartitions exhibit, in their central zone, two portions extendingsubstantially axially and offset circumferentially relative to eachother, together with a third joining portion. The mean variation α inorientation between the third joining portion and the two substantiallyaxially oriented portions is preferably greater than 20 degrees.

Each joining element may be supported on only one side or on both sidesof the supporting element by at least one wall extending substantiallyaxially towards the outside of the annular body.

These axial walls are relatively insensitive to buckling because theyare integral with the supporting element and relatively short. At agiven constant width of the support, these axial walls make it possibleto reduce the width of the supporting element and thus to increase thebuckling resistance thereof.

In a preferred embodiment, a three-branched star structure is formedfrom each joining element with a supporting axial wall and the lateralends of the two adjacent partitions, the axial width of one axial wallbeing less than or equal to half the axial width of the two adjacentpartitions of the supporting element.

The supporting elements according to the invention may also comprise aweb which is substantially cylindrical and coaxial with the support,such web being, for example, arranged radially at half height of thesupporting element. This web is made from the same material as the restof the annular body. When arranged at half height, the web allows theheight of the partitions to be divided by two, thereby approximatelyquadrupling the limit buckling load.

In order to facilitate manufacture of the supports according to theinvention, the various geometries of the supporting elements areadjusted so as to comprise no undercut portions obstructing axialdemolding of the support.

Preferably, a mounted assembly according to the invention for a motorvehicle comprises a wheel rim, a tire mounted on the rim and the supportaccording to the invention. The rim comprises on each of the peripheraledges thereof a rim seat intended to receive a bead of the tire, the rimtherefore having two seats. The rim comprises between the two seats, abearing surface and a mounting groove connecting the bearing surface toan axially internal lip of one of the seats, or first seat.

It will be noted that the flat structure which is imparted to said rimby the bearing surface is such that, during flat running, the entirewidth of the support bears the load, unlike “hollow” type rims.

The aforementioned characteristics of the present invention, as well asothers, will be better understood on reading the following descriptionof several embodiments of the invention, which are given by way ofillustration and not of limitation in comparison with other examples notaccording to the invention.

The above-stated embodiments relating to examples of architecture of thesupport according to the invention are moreover illustrated by theattached drawings, which are discussed in detail below.

In the following examples, flat running tests were performed on supportsaccording to the invention and “control” supports which differ in regardto the composition of the rubber from which they are made and by theselected architecture for these supports.

Referring to FIGS. 1 and 2, each of supports 1 essentially have threeparts:

a base 2, of generally annular shape;

a substantially annular crown 3, optionally having longitudinal grooves5 on the radially external wall thereof, and

an annular body 4 connecting base 2 and crown 3.

FIG. 2 illustrates the function of support 1, namely supporting the tiretread in the event of severe loss of inflation pressure of the tire.

Each tested support was incorporated into a mounted assembly intended toequip a motor vehicle sold under the name “PEUGEOT 806”.

The rim used for this mounted assembly was as is shown in FIG. 2, whichis described above with reference to the preferred mounted assembly ofthe invention. (This rim is also described in detail in French patentspecification FR-A-2 720 977.)

More precisely, the characteristic dimensions (tire width, tirediameter, rim diameter, respectively) of each mounted assembly which wastested are, in mm:

205-650-440.

The characteristic dimensions (width, internal diameter, height,respectively) in mm of each support which was tested are 135-440-50.

For each flat running test (controls and supports according to theinvention), care was taken to ensure that the same relative crushing ofthe support in the radial direction thereof was obtained (this constantrelative crushing being defined as the ratio of deflection to the heightof the support).

The running conditions for each of the tests were as follows:

load on wheel: 530 kg; running speed: 100 km/h; running temperature:between 20° C. and 25° C.

running on a motorway type circuit.

CONTROL EXAMPLES 1) Control Example 1

A first control support which was incorporated into the above-describedmounted assembly for the purposes of the flat running test wasmanufactured from a vulcanized rubber composition as defined below:

elastomer: natural rubber 100 phr; reinforcing filler: “ZEOSIL 1165 MP”silica 54 phr (silica sold by Rhodia exhibiting BET and CTAB surfacearea values of at least 150 to 160 m²/g); coupling agent: Si69/carbonblack N330 8.5 phr* “6PPD”: 2 phr; ZnO: 4 phr; stearic acid: 1 phr;vulcanization accelerator: “CBS”: 3 phr; sulphur: 4.5 phr; where “6PPD”is N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine and “CBS” isN-cyclohexylbenzothiazyl sulphenamide. *(4.25 phr Si69 and 4.25 phrcarbon black N330);

This first control support exhibits an M10 elasticity modulus of 9 MPa(M10 being the standard abbreviation for a secant elongation modulusobtained at a deformation of approx. 10%, at room temperature and on thethird loading cycle, in accordance with Standard ISO 37-1977).

This support is of a known architecture, which is shown in FIG. 13, inrelation to FIGS. 1 and 2.

The section of FIG. 2 shows a first solid portion 4 a of annular body 4together with a second portion 4 b having recesses (c.f. also FIG. 1)extending axially over substantially more than half of annular body 4and opening on the outside in a substantially axial direction. Recesses4 b are distributed regularly around the entire circumference of annularbody 4 and they define partitions 6, which provide a direct radialconnection between crown 2 and base 3 of support 1.

This geometry has the advantage of subjecting partitions 6 to flexuralrather than compressive loads when the partitions are crushed. Recesses4 b and, thus, partitions 6 are sufficient in number to ensure regularsupport during running on the support.

More precisely, this first control support 1 which was tested comprises,around its circumference, 38 partitions 6, each of which exhibits athickness of 18 mm, which are spaced two by two at a distance of 38 mm.

Furthermore, base 2 and crown 3 exhibit a thickness of 7 mm and 8 mm,respectively. The annular body of first control support 1 exhibits, inthe axial direction, a thickness of 35 mm.

The mass of this first control support is 8 kg.

The results of the running test conducted under the above-statedconditions for the mounted assembly comprising this first controlsupport revealed a service life of greater than 200 km.

2) Control Example 2

A second control support which was incorporated into the above-describedmounted assembly for the purposes of the flat running test wasmanufactured from a vulcanized rubber composition which differs fromthat of the first control support in that it comprises a blend ofnatural rubber (60 phr) and polybutadiene (40 phr). The architecture,dimensions and mass of this support were identical to those of saidfirst control support.

This second control support exhibited substantially identical M10modulus values relative to the first control support.

The results of the running test carried out under the above-statedconditions for this mounted assembly comprising this second controlsupport also revealed a service life of greater than 200 km.

Testing was also performed on other control supports manufactured fromcontrol compositions according to control examples 1 or 2, but whichexhibit an architecture as described below with reference to FIGS. 3 to12. The results of the running test carried out under the above-statedconditions revealed a service life for these supports of less than 100km.

Examples of Supports According to the Invention

A series of supports according to the invention was tested. All of thesupports were manufactured from the same vulcanized rubber compositionand exhibited the architectures illustrated in FIGS. 3 to 12,respectively.

For the sake of clarity in the present description, the tested supportarchitectures are presented at the end of the description.

Each support according to the invention was manufactured using thevulcanized rubber composition as follows:

elastomer: natural rubber 100 phr; reinforcing filler: “ZEOSIL 1165 MP”silica 70 phr; coupling agent: Si69/carbon black N330 11 phr;* isotacticpolypropylene: 10 phr; “6PPD”: 2 phr; ZnO: 4 phr; stearic acid: 1 phr;vulcanization accelerator: “CBS”: 3 phr; sulphur: 4.5 phr; (*5.5 phrSi69 and 5.5 phr carbon black N330);

This vulcanized rubber composition is prepared as follows:

In a first thermomechanical working stage performed in a 6 literinternal mixer, all the necessary constituents, including the couplingsystem and various additives, with the exception of the vulcanizationsystem, are kneaded. The elastomer, reinforcing filler and polypropyleneare mixed in the powder state at an initial temperature of 100° C.(elastomer feed temperature), such that the polypropylene is dispersedin the elastomer, with the dropping temperature being approximately 155°C.

In a second mechanical working stage carried out at a temperature ofbelow 100° C., the sulphur vulcanization system is added to the mixtureobtained on completion of the first stage.

In a third vulcanization stage, the mixture obtained on completion ofthe second stage is cured at a temperature of 150° C.

Performing these three stages at temperatures below the melting point ofpolypropylene (168° C.) makes it possible to obtain a dispersion ofnon-fibrillated particles of polypropylene in the elastomer. Moreprecisely, these non-fibrillated particles exhibit a substantiallyspherical shape.

A sieving method was used to determine the particle size distribution ofthe polypropylene powder introduced into the mixer by measuring, for agiven initial mass of polypropylene, the proportion of oversizeparticles on successive passage through the sieves. This method wasperformed in accordance with Standards ISO-1435 and NF-14001.

This particle size distribution was as follows for each sieve, stated incumulative mass fractions relative to the initial mass of polypropylene:

 size < 45 μm; 0.09% size < 125 μm;  5.9% size < 180 μm; 11.4% size <315 μm; 38.3% size < 400 μm; 73.9% size < 500 μm; 99.9% size < 630 μm; 100%.

On this basis, it was concluded that the mean size by weight of theparticles in the rubber composition according to the invention isbetween 50 μm and 500 μm.

Advantageously, each support according to the invention has a mass of 5kg, which is approximately one third less than the 8 kg mass of each ofthe control supports. Thus, each support according to the inventionexhibits a reduced mass relative to the said “control” supports.

Furthermore, the results of the running test carried out under theabove-stated conditions for mounted assemblies comprising supportsaccording to the invention also revealed a service life of greater than200 km.

Each support according to the invention exhibits an MI0 modulus ofapproximately 30 MPa, which imparts thereto a rigidity greater than thatof supports not containing the dispersion.

Moreover, the reinforcing white filler, (silica), in the above rubbercomposition used for each support according to the invention imparts tothe composition improved uncured processing characteristics, as well asimproved cured properties, such as cohesion, in addition to theabove-mentioned rigidity.

Architectures tested in each case for the supports according to theinvention:

A first preferred architecture of the support according to the inventionis illustrated in FIG. 3.

As has been stated above in general terms, with reference to FIGS. 1 and2, a safety support 1 with the architecture depicted in FIG. 3 comprisesbase 2, crown 3 and annular body 4.

FIG. 3 shows a circumferentially continuous supporting element 7 ofpreferred support 1, the supporting element comprising a plurality ofpartitions 6 extending axially on each side of the circumferentialmedian plane P of support 1 and being distributed around thecircumference of support 1.

It may be seen in FIG. 3 that supporting element 7 comprises, on one ofthe sides of support 1, joining elements 8 extending substantiallycircumferentially. Each joining element 8 connects the respective ends 6a of two adjacent partitions 6 which are arranged on said side ofsupport 1, the joining elements 8 being arranged alternately insuccession on each side of partitions 6.

More precisely, joining elements 8 are mutually supported between twoadjacent partitions 6 by a rib 8 a extending from crown 3 to base 2 ofsupport 1, such that joining elements 8 form a continuous joining wall 9in the form of a gusset all along the side of support 1.

More precisely, joining wall 9 comprises a plurality of cells 9 a, eachdelimited by two adjacent ribs 8 a. The bottom of each cell 9 a exhibitsa substantially dihedral shape, the ridge of which is formed by one end6 a of partition 6 and the faces of which are respectively formed byalternate joining elements 8.

There are 40 partitions 6 of support 1 around the circumference ofsupport 1 in this tested example. Each partition exhibits a thickness of8 mm and they are 40 mm apart. As stated above, each support 1 that wastested exhibits a width of 135 mm, a diameter of 440 mm and a height of50 mm.

Base 2 and crown 3 of support 1 exhibit a thickness of 6 mm and 7 mm,respectively.

The distance in the axial direction between a plane P′ in FIG. 3, whichis axially median for joining elements 8, and the respective free endsof ribs 8 a, is 20 mm for this example.

A second architecture of support 1 according to the invention isillustrated in FIG. 4, with FIGS. 5 to 12 illustrating variants of thissecond design (the structural elements analogous to those of FIG. 4 arehereinafter identified by reference numerals incremented by 10 for eachFIG., starting from FIG. 5).

Supports 1 relating to these FIGS. 4 to 12 all comprise base 2, crown 3and an annular body 10.

FIG. 4 depicts an annular body 10 consisting of a circumferentiallycontinuous supporting element 11 which comprises a set of partitions 12connected two by two by joining elements 13.

Partitions 12 extend laterally on each side of the circumferentialmedian plane P of support 1 and they are regularly distributed aroundthe circumference of support 1. They have an angle of inclination A,relative to the circumferential direction, which approaches 90 degrees.The thickness H thereof is constant. Moreover, two adjacent partitions12 have an opposing angle of inclination relative to the axialdirection.

Joining elements 13 have a thickness e and are orientedcircumferentially. Each joining element 13 connects the respective endsof two adjacent partitions 12 which are arranged on the same side ofsupport 1 (these two ends are the ones closest to each other). Joiningelements 13 are thus arranged alternately in succession on each side ofpartitions 12.

It will be noted that, in order to facilitate manufacture of support 1using axial demolding, supporting element 11 comprises no undercutelements.

FIG. 5 shows a variant embodiment of supporting element 21 (compare tosupporting element 11 of FIG. 4).

Partitions 22 of supporting element 21 have a thickness H in theircentral portion which is greater than the thickness h thereof at theirlateral ends. In this example, H is approximately twice the size of h.

This variation in thickness imparts very good buckling resistance to thecentral portions of partitions 22. The lateral ends are connected tojoining elements 23 in continuous manner, which imparts good bucklingresistance thereto.

It will be noted that a variation in thickness of as little as 10% mayhave appreciable effects for the purpose of postponing the onset ofoverload buckling.

FIG. 6 shows another variant embodiment, supporting element 31.

As above, supporting element 31 comprises partitions 32 which areconnected by joining elements 33. Partitions 32 comprise two lateralportions 34 having the same angle of inclination A, relative to thecircumferential direction, which are offset circumferentially and areconnected in the central portion of supporting element 31 by a thirdportion 35 oriented substantially circumferentially.

The mean variation α in orientation between lateral portions 34 andcentral portion 35 is of the order of 80 degrees in this case. Sinceportions 35 are oriented circumferentially, angles α and Δ are equal.

This presence of this third central portion 35, which has a meanorientation differing greatly from that of the two lateral portions,increases the buckling resistance of the central portion of thepartitions 32.

It will be noted that, in order to be effective, variation α must begreater than 20 degrees.

In this embodiment, partitions 32 comprise, from one lateral end to theother, one reversal in the direction of the curvature thereof.

FIG. 7 shows another variant embodiment, supporting element 41.

In this case, joining elements 43, which are arranged on one side ofsupporting element 41, have a circumferential length which is less thanthat of joining elements 44, which are arranged on the other side ofsupporting element 41.

It will be noted that the substantially doubled length of joiningelements 44 increases the compressive stiffness of supporting element 41on this side of the support 1. This latter side should be arrangedtowards the interior side of the vehicle, where the loads borne bysupport 1, while in operation, are the greatest.

FIG. 8 shows another variant embodiment, supporting element 51.

In this case, joining elements 53 are virtually reduced to the contactsurface between two lateral ends 54 as an arc of a circle of partitions52.

Partitions 52 also comprise a central connecting portion 55.

It will be noted that variation α in mean orientation between the twolateral portions 56 and central portion 55 is greater than 90 degreesand is of the order of 110 degrees, which increases the mean supportingdensity of supporting element 51 in the central portion thereof.

From one lateral end to the other, partitions 52 comprise threereversals in the direction of the curvature thereof.

FIG. 9 shows another variant embodiment, supporting element 61, avariant similar to that shown in FIG. 8 with the followingmodifications.

Partitions 62 comprise rectilinear segments and exhibit three reversalsin the direction of the curvature thereof. The partitions comprise twoaxially oriented lateral portions 64, which are connected, on the onehand, by central portion 65 and, on the other hand, to joining elements63 by lateral ends 66 having a mean orientation y approaching 30degrees, relative to the circumferential direction.

Mean variation α in orientation between the two axially orientedportions 64 of partitions 62 and central joining portion 65 is of theorder of 40 degrees.

Joining elements 63 may be defined as elements of a substantiallytriangular cross-section, which are arranged between two adjacentlateral ends 66.

On both sides of supporting element 61, annular body 60 comprises aseries of substantially axially oriented walls 67 which extend eachjoining element 63 towards the outside of support 1. As may be seen inFIG. 9, a three-branched star, which is highly resistant to buckling, isformed where each joining element 63, adjacent lateral ends 66 and axialwall 67 meet.

FIG. 10 shows another variant embodiment, annular body 70 and supportingelement 71.

Supporting element 71 comprises partitions 72 having axially orientedcentral portions 74 which are extended on each side by lateral end 75,which exhibits orientation y approaching 30 degrees relative to thecircumferential direction.

On one side of annular body 70, joining elements 73 are reduced to thecontact surface between two adjacent lateral ends 75. On the other side,annular body 70 comprises lateral walls 76 which support joiningelements 77 on this side, the joining elements being of a substantiallytriangular shape.

It will be noted that on this latter side, the compressive stiffness ofthe supporting element is greater.

The length of lateral walls 76 is, in particular, less than half thelength of central portions 74 of partitions 72, so that they are notliable to buckle.

The side of supporting element 71 having the highest radial compressivestiffness should preferably be arranged on the interior side of thevehicle. It has, in fact, been observed that the loads are highest onthis interior side of the vehicle.

Partitions 72 have a thickness H in their central portion 74 which isgreater than thickness h of their lateral portions 75, so as to increasethe buckling resistance of central portion 74.

FIG. 11 shows another variant embodiment, annular body 80, a variantvery similar to annular body 70 of FIG. 10.

Annular body 80 comprises axial lateral walls 86 and 87 which supportsupporting element 81 on both sides the supporting element 81 also beingstructurally similar to supporting element 71 of FIG. 10.

For a given width of annular body 80, lateral walls 86 and 87 exhibitthe advantage of reducing the axial width of partitions 82 of continuoussupporting element 81 and thus of improving the buckling resistance ofthe overall structure. The axial lengths of walls 86 and 87 may differ,as illustrated in FIG. 11.

FIG. 12 shows an axial view of a support 1 including a supportingelement 91, analogous to the supporting element of FIG. 11, butadditionally comprising circumferential web 94, which is arranged athalf height of annular body 90. Circumferential web 94, of cylindricalshape, provides the advantage of bringing about a very substantialincrease, of the order of a factor of four, in the limit buckling loadof the structure of support 1.

Each of the supports 1 described with reference to FIGS. 4 to 12exhibits the following dimensional characteristics.

There are 40 partitions (designated 12 . . . 92 in FIGS. 4 to 12,respectively) around the circumference of each support 1. Each partitionexhibits a thickness of 8 mm and they are 40 mm apart. As stated above,each tested support 1 exhibits a width of 135 mm, a diameter of 440 mmand a height of 50 mm.

Furthermore, base 2 and crown 3 of support 1 exhibit a thickness of 6 mmand 7 mm, respectively.

All supporting elements (designated 7, 11 . . . 91 in the Figures) andannular bodies (designated 4, 10 . . . 90 in the Figures) may bemanufactured from the vulcanized rubber composition of the invention bymolding techniques. In order to facilitate axial demolding, theypreferably comprise no undercut portions.

It will be noted that it would also be possible to use, as a supportarchitecture according to the invention, a support having two or morerings connected together in the axial direction of the support, theoverall structure thereof remaining unchanged.

It could, for example, be possible to provide for such a support a firstring having a substantially rectangular axial section, and one or moreannular elements comprising a plurality of recesses and extendingsubstantially axially across the entire width thereof and distributedsubstantially regularly around the circumference thereof.

Such a ring-type support is easier to introduce into a tire, due to thelower flexural rigidity of the various annular elements thereof.

We claim:
 1. A rubber composition which, when vulcanized, is usable in asafety support intended to be mounted on a wheel rim inside a tire, thecomposition comprising: (a) a diene elastomer, (b) particles of anα-olefinic thermoplastic polymer having a melting point greater than orequal to 150° C, in an amount of 5 to 30 parts by weight per 100 partsdiene elastomer (phr), wherein the mean size by weight of the particlesis between 30 μm and 500 μm, (c) greater than 60 phr of reinforcingfiller, and (d) from 3 to 8 phr of sulphur, wherein the particles ofthermoplastic polymer are dispersed within the diene elastomer.
 2. Therubber composition of claim 1, wherein the reinforcing filler comprisesgreater than 50% reinforcing white filler.
 3. The rubber composition ofclaim 2, wherein the reinforcing white filler is silica in an amountranging from 60 to 80 phr.
 4. The rubber composition of claim 2, furthercomprising a polysulphurized alkoxysilane reinforcing whitefiller/elastomer bonding agent.
 5. The rubber composition of claim 1,wherein the α-olefinic polymer is isotactic polypropylene.
 6. The rubbercomposition of claim 1, wherein the diene elastomer is either naturalrubber or synthetic polyisoprene.
 7. The rubber composition of claim 1,wherein the diene elastomer is a blend of: (a) natural rubber orsynthetic polyisoprene in an amount greater than or equal to 60 phr, and(b) a homopolymer obtained by polymerization of a conjugated dienemonomer having from 4 to 12 carbon atoms or a copolymer obtained bycopolymerization of one or more conjugated dienes with each other orwith one or more vinyl aromatic compounds having from 8 to 20 carbonatoms, in an amount of less than or equal to 40 phr.
 8. The rubbercomposition of claim 7, wherein the blend comprises approximately 60 phrof natural rubber and approximately 40 phr of polybutadiene.
 9. Therubber composition of claim 1, wherein the composition exhibits an M10elasticity modulus at 10% deformation which is greater than 10 MPa. 10.The rubber composition of claim 1, wherein the α-olefinic polymer isdispersed in the elastomer in the form of substantially sphericalparticles.